Just a little strange idea for crumbly elements. Maybe you know how crumbled elements connects only horizontally or only vertically. But that system is not always useful because if it copies side of border so for some more unique walls it will be problematic to connect them. Try to do this with basic walls or steel walls. Their corners after connecting only vertically or horizontally will copy the sides of borders and walls will be broken.
But what if you'll make them use two more tiles like "Only vertical" and "Only horizontal"? And use them like "inner_corners" by '.frames: 4' (normal crumble with outer corners, crumbling inner corners, and then only horizontal and only vertical in any order or not). I would also perfectly affect to [border_size <= half of tile_size].

I think it would be very nice and almost perfect feature for professional RND-graphics makers!
But sorry that I told you this pretty badly and didn't even show any examples, I just wrote it on my phone...